This project examines the neurophysiology and the neuropharmacology of connections between the dorsal and ventral hippocampal formation, and the hypophysiotrophic areas of the hypothalamus in the rat. Extracellular recording techniques will be used to examine the synaptic connections between the hippocampal formation and the hypothalamus, with special attention to buberoinfundibular neurons, i.e. neurons with median eminence axon terminals that function to regulate anterior pituitary secretion. Elucidation of the neurophysiology of hippocampal connections with medial hypothalamic and medial preoptic tuberoinfundibular neurons is considered important for an understanding of the mechanisms of hippocampal regulation of endocrine function. These connections will be compared with those of another limbic structure, the amygdala known to affect endocrine function.